1. n. []

A type of oxygen activation technique for measuring water flow in which a short neutron burst is followed by a long observation period, during which the activated flowing oxygen is recognized at the detector by its signature. Stationary oxygen gives a gradually decaying signal, whereas flowing oxygen can be distinguished by a peak at a time after the neutron pulse that is related to its velocity. To cover a wide range in water velocity, several detectors at different spacings are needed. The flow volume can be estimated from the area under the peak. While recordings are typically made with the tool stationary, continuous logs are also possible. In an alternative type of impulse method, the neutrons are emitted in regular bursts until the count rate from the activated oxygen reaches a constant level. Then, after terminating the bursts, the time for the count rate to decrease by one half is measured. This time can be related to the water velocity.

See related terms: activation log,  neutron capture,  neutron generator,  pulsed neutron spectroscopy measurement